Cathode ray intensity control system



D. PRINZ CATHODE RAY INTENSITY CONTROL SYSTEM Filed Dec. 15, 1931 RADIOFREQUENCY AMPLIFIER Aug. 13, .1935.

HFIH HH HHHHW Maul/14750 mg i A A n Patented Aug. 13, 1935 UNITED STATESFATE T OFFICIE Telefunken Gesellschaft fur Drahtlose Telegraphic m. b.H., Berlin, Germany, a corporation of Germany Application December 15,1931, Serial No. 581,217 In Germany December 15, 1930 3 Claims.

The present invention relates to television systems and is directedprimarily to the use of cathode ray or Braun tubes for the purpose ofrebuilding or reconstructing the electro-optical television image.

It is known to those trained in this art that arrangements of this sortmay be attended with the difliculty of varying the brightness orluminosity of the image spot produced upon the fluorescent end wall orscreen of the tube by the cathode ray without incidentally varying alsothe position thereof. To overcome this diificulty, according to thepresent invention, a hole or aper ture diaphragm is mounted between theanode and the control or deflecting electrostatic plates orelectromagnetic fields of the Braun or cathode ray tube which will justallow of the passage of the cathode ray, while between the anode and thesaid apertured diaphragm there is interposed a pair of control plates towhich a radio frequency alternatingcurrent potential is applied directlyfrom the receiver. As a result, conditions are made so that the cathoderay penoil is able to pass through the apertured dia phragm only duringa fraction of a cycle of the radio frequency potential.

Inasmuch as the speed at which the ray moves past the apertureddiaphragm is proportional to the amplitude of the radio frequency, itfollows that the time for which the ray has a chance to pass through thediaphragm is inversely proportional to the amplitude of the radiofrequency energy. The same thing holds true of the brightness of thespot upon the fluorescent screen since the spot brilliance isproportional to the length of time during which the cathode ray pencilimpinges upon the fluorescent end wall or screen of the tube.

Since the cathode ray passes through the apertured diaphragm just duringa time when the de fleeting radio frequency potential passes substantially through zero, it will be seen that the electrons issuing fromthe source at that particular instant are entirely uninfluenced so thatthey will be deviated by the control plates of the Braun tube in justthe same manner as if the radio frequency potential were not present atall. As a matter of fact, the position of the spot will not be affectedduring this particular period of variation of the brightness thereof.

If the transmission of the television picture is effected by the aid ofradio frequency oscillations, then the incoming radio frequencyoscillations, preferably amplified to some extent at least, withoutprior rectification, may be fed directly to the auxiliary control platesof the cathode ray or Braun tube.

Modulation of the transmitter should be effected in such a way that theradiated radio frequency energy is inversely proportional to thebrightness of the picture point or unit to be transmitted.

It is known in the art that the luminosity of the light spot producedupon the fluorescent end wall of a cathode ray or Braun tube may bevaried by slightly deviating the cathode ray pencil passing through thediaphragm out of its normal position or path, so that only a part of theelectrons is able to pass through the aperture of the diaphragm. In anarrangement of this sort, however, the cross-section of the pencil ofcathode rays must be perfectly homogeneous in order that a state ofproportionality may be secured between luminosity and deflection. Thisdifliculty has been avoided in the present arrangement, for the solepoint to be satisfied is that the entire cathode ray should pass acrossthe diaphragm.

Other novel features and advantages of the present invention will becomeapparent and suggest themselves from a reading of this specification andclaims in connection with the accompanying drawing, wherein the singlefigure illustrates in diagrammatic manner one form of system forreconstructing electro-optical images using the above suggested form ofimage intensity control.

Referring now to the accompanying drawing, wherein Fig. 1 representsschematically a system according to the present invention, and whereinFig. 2 plots the modulated radio frequency re ceived signal amplitudeagainst time and indicates the width of the aperture in the diaphragm,and also wherein the active period of the ray pencil upon thefluorescent screen is indicated in the same time relationship as themodulated radio frequency signal, signals originating at a transmittingpoint are picked up at the receiving station by any appropriate type ofantenna or signal collector I and transferred therefrom to a radiofrequency amplifier 3. For the purpose of reconstructing anelectro-optical image representation of the received image signals, acathode ray or Braun tube 5 is provided. Within one end portion of thetube 5 is a cathode I, which may be either the heated or the cold type,appropriately shielded by a shielding element 9. The cathode ray IIwhich is emitted from the cathode 1 is then'projected longitudinally ofthe tube through the anode element l3, which is appropriately groundedat i5, and the diaphragm element I! and 23 are provided. Thesedeflecting plates are supplied with suitable electric potentials soarranged as to cause the cathode ray beam to traverse the screen in twodirections, for example, the plates 2| may cause a rapid traversal fromleft to right to represent horizontal image points and the plates 23 maycause a slower motion of the cathode ray along a path at right angles tothe deflection path produced by the plates 2|. This deflecting field maybe of the well-known saw-tooth type, so that there is a relatively slowtraversal in one direction and practically an instantaneous'return inorder that the image is reproduced always in one direction.

Since the manner of producing the deflecting fields forms no part of thepresent invention, no specific form is shown, but it is understood thatany well known type of means to produce deflecting fields may be used.For these two deflecting fields, it should be understood that the lowerof the two deflecting frequencies, that is the frequency causing theslow motion, should be of a frequency equal to the number of picturerepetitions per second. Therefore, this lower frequency may, forexample, be of a value varying between 16 and 24 cycles per second andthe higher of the two frequencies will be a value equal to the lowerfrequency multiplied by the number of picture lines forming eachreproduced image, so that the higher frequency, for example, may vary,assuming a 100 line picture is being constructed, from 1600 cycles persecond to 2400 cycles per second, depending upon the number of completepictures per second which are to be reproduced. In any case, however, itis to be understood that these values are merely suggested as suitablebut are not in any sense intended to be limiting.

Also, while electrostatic ray deflection within the tube for positioncontrol has been shown, it is likewise possible to substitute for theelectrostatic deflection electromagnetic deflecting fields which, ifdesired, may be external to the tube, and also to substitute externalelectrostatic-deflecting fields.

In order to produce modulation of the resulting light spot produced bythe bombardment of the fluorescent end wall IQ of the tube 5 by thecathode ray ii, an auxiliary pair of plates 25 has been provided. One ofthese plates is connected to ground at l5, for example, and the otherplate is connected with the radio frequency amplifier circuit by meansof a suitable conductor 21,50 that the amplified radio frequencyoscillations received by the collecting means I may be impresseddirectly upon the intensity controlling deflecting plates 25. As wasabove set forth, this arrangement will produce a control of theintensity of the resulting light spots upon the fiuorescent screen,since the time during which the cathode ray stream II is able to passthrough the diaphragm I! in its passage toward the fluorescent end walll9 of the tube is proportional to the amplitude of the supplied radiofrequency energy and the brilliance of the spot upon the fluorescentscreen is, in turn, proportional to the time during which the cathoderay impinges thereon.

Other modifications of this invention to produce a suitable intensitycontrol of the resulting.

electro-optical image produced upon the fluorescent end wall of the tubeare, of course, obvious to anyone skilled in the art to which theinvention relates, and therefore the invention herein disclosed is to beconsidered in its broad sense as covering all forms of intensity controlwhich fall fairly within the spirit and scope of the present disclosure,as defined by the hereinafter appended claims.

Having now described my invention, what I claim and desire to secure byLetters Patent is the following:

1. In a television system embodying a cathode ray tube and a set ofauxiliary deflecting plates arranged to control the passage of thecathode ray through a diaphragm toward the fluorescent screen, themethod of reproducing television signals which comprises generating acathode ray and projecting the generated ray toward the fluorescent endwall of the tube for producing luminous spots thereon, producing aposition controlled deflection of the resulting spots along a pair ofpaths transverse to each other at appropriate speed rates, and supplyingto the intensity controlling defiecting plates radio frequencypotentials to control in accordance with the amplitude of the suppliedpotentials the time of passage of the cathode ray through the dia phragmto impinge upon successive elemental sections of the screen.

2. In a-television receiving system comprising the combination of acathode ray tube provided with a fluorescent end wall adapted to producelight spots upon the bombardment thereof by cathode rays, the method ofintensity control which comprises limiting the normal period duringwhich the cathode rays impinge upon the fluorescent end wall to producelight spots within the cathode ray tube, and varying the said normaleffective time period of impact of said rays by influencing the cathoderay in its passage toward the fluorescent screen with an amplitudevarying radio frequency field proportional in amplitude to fluctuatingintensities of light and shadow to be represented.

'3. In a television system, a cathode ray tube having a fluorescent endwall, an apertured diaphragm within the tube, a pair of signal actuateddeflecting plates arranged to control the passage of the cathode raythrough the aperture toward the fluorescent end wall, means forproducing a plurality of transverse electric fields within the tube tocause the light spots produced from the cathode ray acting upon thefluorescent material to trace upon the end wall of the tube a pair ofpaths at right angles to each other at appropriate speed rates, andmeans for sup-

